1. Field of the Invention
The present invention relates to spindle motors mounted in, for example, information devices or acoustic devices which require precise rotation, and in particular, relates to spindle motors to be used in HDDs (hard disk drives) in magnetic disc units.
2. Related Art
As precise rotation motors used in, for example, HDDs, there have been provided constructions in which a disk is rotated with high precision by a brushless dynamotor. Bearings suitable for these motors comprise a combination of a radial bearing and a thrust bearing respectively supporting the radial load and thrust load of the rotating shaft as proposed in Japanese Patent Applications, First Publications Nos. 1995-12127 and 2000-81030. These bearings are generally fluid dynamic bearings in which the rotating shaft is supported with high precision due to the dynamic pressure action of a lubricant.
HDD motors mounted in personal computers require high rotation precision. In particular, HDD motors mounted in notebook personal computers require an even higher level of quietness and impact resistance, and it is also desirable to reduce the thickness thereof according to the performance requirements of the final product. Fluid dynamic bearings are able to yield high precision rotation due to the dynamic pressure action of a lubricant and are effective for quietness since the rotating shaft is supported in a non-contact manner, and they have therefore begun to be used for bearings in HDD motors. The impact resistance is ensured by positioning the rotating shaft in the axial direction so as to prevent damage to a magnetic head and a magnetic disk. Means for positioning and restraining displacement of the rotating shaft in the axial direction such as a flange formed thereto and engaging with the bearing is generally provided as in the motors disclosed in the above references. Since HDDs require that no oil leaks, there have been proposed bearings comprising a combination of a magnetic fluid and a permanent magnet.
The above construction for restraining displacement of the rotating shaft supports impact load by the bearing. When the bearing receives an impact corresponding to 1000 G, the bearing may move approximately 10 xcexcm in the axial direction. Such a slight movement of the bearing may damage the head and the disk, and information cannot be written thereto; such a movement of the bearing must therefore be prevented.
Therefore, an object of the present invention is to provide a spindle motor which ensures sufficient levels of quietness and rotation precision.
Another object of the invention is to provide a spindle motor capable of ensuring rigid positioning of the rotating shaft in the axial direction with a simple construction while achieving extremely high impact resistance.
Another object of the invention is to provide a spindle motor allowing for a reduced thickness of the product and minimizing the number of parts.
The present invention provides a spindle motor comprising: a housing including a through hole with a pair of apertures at both ends thereof, one of the apertures being closed by a thrust plate and the other aperture being open; a bearing accommodated in the through hole of the housing; a rotating shaft inserted into the bearing, a radial load and a thrust load thereof being respectively supported by the bearing and the thrust plate; a displacement restraining structure for restraining movement of the rotating shaft toward the open aperture by engaging the rotation shaft with the bearing; a rotating member secured to the rotating shaft; and a motor generating electromagnetic function for rotating the rotating member. A lubricating fluid is provided between the bearing, and the rotating shaft and the thrust plate. The through hole of the housing includes a large diameter portion at the thrust plate side and a small diameter portion at the open aperture side, and a stepped portion is formed at a transition portion between the large diameter portion and the small diameter portion. At least a portion of the bearing is located at the large diameter portion side of the housing, and engages with the stepped portion of the housing.
According to the invention, the radial load and the thrust load of the rotating shaft are respectively supported by the bearing and the thrust plate, and a lubricating fluid is provided to the respective supporting surfaces. Therefore, the rotating shaft is supported by the bearing and thrust plate in a non-contact manner, and quietness and precise rotation are sufficiently ensured.
The rotating shaft in the invention receives a floating force from the thrust plate due to the hydraulic pressure of the lubricating fluid provided between the rotating shaft and the thrust plate. In this condition, the rotating shaft is positioned in the axial direction since the rotating shaft is restrained from moving toward the open aperture of the housing by engaging the displacement restraining structure with the bearing. The bearing is restrained from moving toward the open aperture of the housing since at least a portion of the bearing engages with the stepped portion of the housing. By the combination of these functions, rigid positioning of the rotating shaft in the axial direction is ensured, thereby achieving extremely high impact resistance. These functions and advantages are obtained by forming the stepped portion in the housing and engaging the bearing with the stepped portion. Therefore, the invention does require a large number of parts and complicated structures, thereby allowing for a reduced thickness of the product.
The displacement restraining structure in the invention may be a flange formed at the thrust plate side of the rotating shaft and may be adapted to engage with an end surface at the thrust plate side of the bearing.
The present invention includes an embodiment in which an elastic member is provided between the bearing and the thrust plate. In the embodiment, the elastic member seals the clearance between the thrust plate and the housing, and the leakage of the lubricating oil can thus be prevented.
In the embodiment having the elastic member, the displacement restraining structure may comprise a stopper ring provided between the bearing and the elastic member, and a peripheral groove which is formed on an outer surface of the rotating shaft at a location opposing the stopper ring and engages with the stopper ring. In the embodiment, the stopper ring engages with the peripheral groove, and the rotating shaft engages with the bearing via the stopper ring, whereby positioning in the axial direction is performed.
It should be noted that at least a portion of the bearing is provided at the large diameter side of the housing in the invention. The invention includes an embodiment in which a bearing is further provided at the small diameter side of the housing. The bearings in this embodiment may be an integrally formed bearing extending between the large diameter side and the small diameter side of the housing, or they may be plural bearings divided at the large diameter side and the small diameter side.
In the embodiment in which the plural bearings are separately located at the large diameter side and the small diameter side of the housing, a magnet may be provided between the bearings, and the lubricating fluid may be a magnetic fluid. According to the embodiment, the magnetic fluid is usually held in lubricating fluid paths, and the leakage of the lubricating fluid can be prevented. The location of the magnet is not limited to the above manner. The magnet may be located between a portion of the bearing located at the large diameter portion of the housing and the stepped portion of the housing.
As other embodiments which can be anticipated to have the same function as the above, the bearing may be a composite bearing installed with a magnet therein, or may be a magnetic powder mixed bearing in which a magnetic powder is dispersed. A magnetic fluid is used for the lubricating fluid in each case.
According to a preferred embodiment of the invention, the bearing has an end surface at the open aperture side of the housing, and the end surface is recessed from an edge of the open aperture of the housing. For example, when a volume increase occurs in the lubricating fluid due to temperature change, the fluid surface rises up to the end surface of the bearing at the open aperture side of the housing, and the lubricating fluid percolates therefrom. In the embodiment, the percolated fluid on the end surface of the bearing will be blocked by the inner surface of the housing, which surface is exposed to the end surface of the bearing, and the fluid will be held there as a reserve. When the volume of the fluid decreases, the fluid will return to the lubricating paths. Therefore, leakage of the lubricating fluid can be prevented and smooth circulation thereof can be maintained.